Search algorithms based on eliminating-highest-error and fastest-metric-descent criteria for bit-synchronous CDMA multiuser detection

In Sun (1998), the fastest-metric-descent (FMD) and eliminating-highest-error (EHE) criteria were proposed for the improvement of iterative algorithms for bit-synchronous CDMA multiuser detection. In this paper, the EHE and FMD criteria are proposed to apply to search algorithms. The FMD and EHE criteria applicable to the search algorithm are presented. It is shown that at each bit demodulation, the FMD criterion achieves the largest amount of metric descent, while the EHE criterion achieves the largest correct demodulation probability. Two search algorithms are proposed based on the FMD and EHE criteria, respectively. Analysis shows that the FMD and EHE search algorithms have advantages for the systems near perfect power control, but suffer from the near-far problem. Then we propose that the FMD and EHE search algorithms are followed by the FMD and EHE iterative algorithms, respectively, which are near-far resistant and guarantee to achieve local minimum points of the metric. Simulation results show that the FMD and EHE search algorithms performed much better than the original search algorithm in perfect power control. The FMD and EHE search-iterative algorithms show even better performance in all situations. All proposed algorithms have linear computational complexity.